Pressure sensor header having an integrated isolation diaphragm

ABSTRACT

A pressure sensor header for a pressure transducer includes a header shell having a sensor cavity formed therein, a sensor element disposed in the sensor cavity, a fluid medium disposed in the sensor cavity, an isolation diaphragm closing the sensor cavity, and a joining arrangement disposed at an interface of the isolation diaphragm and the header shell, the joining arrangement joining the isolation diaphragm with the header shell. The isolation diaphragm is an integral unit comprising a thin membrane surrounded by a thicker outer ring. The joining arrangement has a recessed female joining element formed in one of the outer ring of the isolation diaphragm and the header shell, and a protruding male joining element formed on the other one of the outer ring of the isolation diaphragm and the header shell, the male joining element received in the female joining element.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/339,725 entitled, “Pressure Sensor Header Having anIntegrated Isolation Diaphragm” and filed on Jan. 9, 2003.

FIELD OF THE INVENTION

The present invention relates to pressure transducers, and moreparticularly, to a pressure sensor header having an integrated isolationdiaphragm which is joined with the shell or body of the header via atongue and groove joining arrangement.

BACKGROUND OF THE INVENTION

Pressure transducers normally include pressure sensor headers. See forexample, U.S. Pat. No. 4,695,817 entitled, ENVIRONMENTALLY PROTECTEDPRESSURE TRANSDUCERS EMPLOYING TWO ELECTRICALLY INTERCONNECTEDTRANSDUCER ARRAYS issued to A. D. Kurtz et al. on Sep. 22, 1987 andassigned to the assignee herein. Certain pressure sensor headers includea metal header shell that defines a sensor cavity. The sensor cavityhouses a sensor element and contains a fluid medium, which at leastcovers the sensor. The sensor cavity is hermetically sealed with anisolation diaphragm that is welded to the header shell.

In normal operation, the fluid medium transmits pressure from theisolation diaphragm to the silicon sensing diaphragm of the sensor.Silicone oil is usually selected as the fluid medium because it exhibitsminimum compressibility, and thus, allows accurate transmission ofpressure without nonlinearities or dead-bands.

Pressure transducers may be employed in high pressure environments. Forexample, pressure transducers are used for monitoring pressure in powergenerating pumps. The pressure sensor headers of these transducers oftenoperate under external (hydrostatic) pressures, which can reachextremes, up to and in excess of 50,000 psi. These pressures act on thefront face and side wall of the header. The pressure force acting on theheader shell's cylindrical side wall generates compressive tangentialand radial stresses (hoop stress) in the side wall. Although pressuresensor headers can be helium leak tested and qualify as hermetic, suchsensors used in the presence of hydrogen gas can leak, allowing theintroduction of hydrogen into the oil-filled sensor cavity, as thehydrogen molecules are much smaller than helium molecules.

A possible entry path for the hydrogen is the isolation diaphragm weld.Conventional designs employ a laser welding process to hermetically sealthe isolation diaphragm to the header shell. In this welding process,the diaphragm is positioned on the header shell and spot welded. Thediaphragm is then fully laser welded to the header shell using aconventional lap or partially penetrating weld. Under excessive cyclicoperation, the weld area experiences high stress, which tends to causethe propagation of very small cracks in these shallow, conventional lapor partially penetrated welds joining the isolation diaphragm with theheader shell. The stress may result in weld fracture and fatiguefailure, thus, presenting an entry point for the hydrogen gas molecules,which are much smaller than helium gas molecules. Thus, over time, thehydrogen gas can penetrate the very small cracks in the shallow,conventional welds.

When hydrogen gas is introduced into the oil-filled sensor cavity, thesystem pressure must first compress the hydrogen gas, beforetransmitting the pressure through the silicone oil. This gas compressionpresents a dead-band at low pressures, and causes a non linear effect onthe sensor output.

Thus, a pressure sensor header is needed which has an integratedisolation diaphragm and diaphragm/header shell weld area that preventsentry of hydrogen gas into the sensor cavity under excessive cyclicoperation in extreme external pressures.

SUMMARY OF THE INVENTION

A first aspect of the invention involves a pressure sensor header for apressure transducer. The header comprises a header shell having a sensorcavity formed therein, a sensor element disposed in the sensor cavity, afluid medium disposed in the sensor cavity, an isolation diaphragmclosing the sensor cavity, and a joining arrangement disposed at aninterface of the isolation diaphragm and the header shell, the joiningarrangement joining the isolation diaphragm with the header shell. Thejoining arrangement comprises a recessed female joining element formedin one of the isolation diaphragm and the header shell, and a protrudingmale joining element formed on the other one of the isolation diaphragmand the header shell, the male joining element received in the femalejoining element.

A second aspect of the invention involves the isolation diaphragm whichmay be an integral unit comprising a thin membrane surrounded by athicker outer ring. The recessed female joining element may be formed inone of the outer ring of the isolation diaphragm and the header shell,and the protruding male joining element may be formed on the other oneof the outer ring of the isolation diaphragm and the header shell.

A further aspect of the invention involves a pressure transducerassembly comprising the pressure sensor header described above joinedwith a second transducer assembly member.

A further aspect of the invention involves a method of joining anisolation diaphragm with a header shell of a pressure sensor header. Themethod comprises the steps of providing a protruding male joiningelement on one of the header shell and the isolation diaphragm,providing a recessed female joining element on the other one of theheader shell and the isolation diaphragm, assembling the isolationdiaphragm to the header shell at a isolation diaphragm-header shellinterface so that the male joining element is disposed in the femalejoining element, and welding the isolation diaphragm and the headershell at the interface.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference is made to thefollowing description taken in connection with the accompanyingdrawings, in which:

FIG. 1 is a sectional view of an illustrative pressure sensor headermade according to the principles of the present invention.

FIG. 2 is an enlarged view of the area circled of FIG. 1.

FIG. 3 is an exploded, sectional view of a portion of the header in FIG.1.

FIG. 4 is a sectional view of a pressure transducer assembly thatutilizes a pressure sensor header made according to the principles ofthe invention.

FIG. 5 is a sectional view of a portion of a conventional pressuretransducer assembly showing how stress causes crack propagation at thediaphragm-header shell interface.

FIG. 6 is a sectional view of a pressure sensor header utilizing thetongue and groove isolation diaphragm to header shell joiningarrangement of the present invention, showing how the joiningarrangement takes advantage of hoop stress to stop crack propagation atthe diaphragm-header shell interface.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an illustrative embodiment of a pressure sensor header 10made according to the principles of the present invention. As shown, thepressure sensor header 10 includes a body or shell 11, which istypically made from a metal or metal alloy. The shell 11 has a front end12, an opposing back end 14, a stepped side wall 16, and a cylindricalbore 17 with a inwardly directed annular flange 19 at the back end 14. Afused, glass seal or bead 28 is disposed in the bore 17 of the shell 11,and seated on the flange 19. The shell 11 and glass bead 28 define asensor cavity 18, which faces the front end 12 of the shell 11. Thesensor cavity 18 contains a sensor element 22, which may be centrallymounted on the glass bead 28, the top surface of which forms a floor 20of the sensor cavity 18. A plurality of cylindrical apertures 24 extendthrough the glass bead 28 and communicate with the sensor cavity 18. Anumber of the apertures 24 contain a pin 26. The pins 26 are typicallyconstructed of a gold-plated, glass sealing alloy, such as Kovar. Thefused glass bead 28 forms a glass-metal seal 30 with each pin 26. Theglass-metal seals 30 hermetically seal the pins 26 to the shell 11, thuspreventing pressure medium (not shown) leakage from the front end 12 ofthe shell 11 to the back end 14 of the shell 11. The fused, glass bead28 also dielectrically insulates the pins 26 from the shell 11. A tube32 is also disposed in one of the apertures 24. The tube 32 allows thesensor cavity 18 to be filled with a suitable fluid medium, such assilicone oil, after which the tube 32 may be sealed by welding or otherconventional sealing means.

Leaded or leadless sensor methods can be used for electrically couplingthe sensor element 22 to the header pins 26. In the shown embodiment, aleadless sensor method in the form of gold frit layers 34 is used forelectrically coupling the sensor element 22 to the header pins 26.Embodiments which utilize leaded sensor methods may use gold bond wires(not shown) to electrically couple the sensor element 22 to the pins 26.

In a further embodiment of the present invention (not shown), the glassbead 28 of FIG. 1, may be replaced by a metal floor which may be unitarywith the shell. The pin and tube apertures may extend through the metalfloor. Glass beads may be used around the pins to seal them to the metalfloor and dielectrically isolate them from the shell.

The shell 11, adjacent the front end 12 thereof, includes a rim-likeannular flange surface 40 which mounts an isolation diaphragm 42 havingopposing outer and inner sides 44, 46. The isolation diaphragm 42hermetically seals the sensor cavity 18 and also forms a front face ofthe pressure sensor header 10. The isolation diaphragm 42 includes athin membrane 49 surrounded by and unitary or integral with acomparatively thicker outer ring 51. Typically the thickness of thediaphragm is between 0.002 and 0.005 inches. The thickness and diameterare selected according to the desired application, pressure range, andsensitivity. The added thickness of the outer ring 51 (relative to themembrane 49) is provided on the inner side 46 of the isolation diaphragm42. The added thickness is provided on the inner side of the diaphragm,to increase the distance of the thin diaphragm member from the heataffected zone of the weld area in the thick region. Increasing thedistance from the weld area prevents thermal stresses from buckling ordamaging the thin diaphragm member. Placing the added thickness on theouter side of the diaphragm would place the thin diaphragm in line withthe heat affected zone, allowing the diaphragm to be damaged during thewelding process. The isolation diaphragm 42 of the present inventionprovides very high sensitivity and accuracy for the pressure range ofthe transducer to be designed. The integral membrane/ring constructionof the isolation diaphragm 42 eliminates weld stresses and heat affectedzones in the highly stressed outer periphery 52 of the thin membrane 49.

In accordance with the present invention, the isolation diaphragm 42 isjoined to the annular flange surface 40 of the shell 11 by a tongue andgroove joining structure or arrangement. As best shown in FIG. 2, thetongue and groove joining arrangement includes a ring-shaped tongue orprotruding male element 48 formed on the annular flange surface 40 ofthe header shell 11. The tongue 48 is typically positionedconcentrically with the side wall 16 of the shell 11. As per the shownembodiment, a mating or matching ring-shaped groove or recessed femaleelement 50 is formed in the inner surface 47 of the isolation diaphragmouter ring 51. Alternatively, the tongue and groove joining arrangementmay include a tongue (not shown) formed on the inner surface 47 of theisolation diaphragm outer ring 51 and a corresponding groove (not shown)formed in the annular flange surface 40 of the header shell 11. Thetongue 48 is formed to fit tightly (conventional slip-fit or press-fit)within the groove 50, upon assembly of the isolation diaphragm 42 withthe shell 11, to create a weld area 54 at the diaphragm-header shellinterface 52 suitable for electron-beam welding or other known weldingmethods.

Referring to FIG. 3, the tongue 48 is typically configured to have arectangular-shaped cross-section, such that the tongue 48 protrudesperpendicularly from the annular flange surface 40 of the header shell11 and has three groove mating surfaces 48 a, 48 b, 48 c, which aresubstantially orthogonal relative to each other. The matching groove 50would also be configured in a rectangular-shaped cross-section withthree tongue mating surfaces 50 a, 50 b, 50 c. The tongue and matchinggroove may also be configured in cross-sectional shapes other thanrectangular, such as semicircular or triangular.

The tongue and groove joining arrangement may also include two or moregrooves or combination of groove(s) and tongue(s) formed in and/or onone of the annular flange surface 40 of the header shell 11 or innersurface 46 of the isolation diaphragm 42 and a matching number oftongues or combination of tongues and grooves formed in and/or on theother one of the annular flange surface 40 of the header shell 11 orinner surface 46 of the isolation diaphragm 42. The tongue and groovejoining arrangement may also be implemented with other male-female typejoining configurations.

Referring again to FIG. 2, the tongue and groove joining arrangement ofthe present invention permits a full penetration weld 56 (to the tongue48) to be made in weld area 54. Weld 56 extends through thediaphragm-header shell interface 52 to the respective mating surfaces 48c, 50 c of the tongue 48 and groove 50. Hence, the tongue and groovejoining arrangement increases the weld depth, as compared withconventional butt welds or partial welds, thereby increasing the jointstrength without the need for increasing the actual wall thickness ofthe header shell 11.

The pressure sensor header 10 of the present invention may be utilizedin a pressure transducer assembly, such as the one shown in FIG. 4. Inthe shown pressure transducer assembly, denoted by numeral 60, thepressure sensor header 10 is joined with a port 62. In other transducerassemblies, the pressure sensor header 10 may be joined with othertransducer assembly members, such as the sensor body.

As mentioned earlier, high bending stresses tend to cause crackpropagation in conventional lap or partially penetrated welds joiningthe isolation diaphragm 42 with the header shell 11, which eventuallyresults in weld fracture and subsequent hydrogen infiltration into thesensor cavity 18. The tongue and groove arrangement of the inventionsubstantially eliminates such problems because, unlike conventionaljoining methods such as lap welds or partial penetration welds, thetongue and groove arrangement of the invention aids in preventing crackpropagation under static or cyclic loading conditions. In the case of aconventional partial depth lap weld joining arrangement, as shown inFIG. 5 and denoted by numeral 70, cracks 74 (only one shown) in the weld70 frequently occur along the inner circumference 72 of thediaphragm-header shell interface 76. The applied cyclic external(hydrostatic) pressure N generates bending stress forces C, whichoperate to open the cracks 74. Under cyclic pressure conditions, thisrepeated force will continue to open the crack 74, with each cycle,thus, allowing hydrogen gas to eventually penetrate into the sensorcavity.

However, as shown in FIG. 6, the tongue and groove joining arrangementof the present invention turns the direction of the cracks 80 (only oneshown) 90 degrees so that the leading ends or crack tips 80 a of thecracks 80 will be along the outer cylindrical surfaces 48 c, 50 c of thetongue and groove joining arrangement. The weld and bending stress areremoved from the thin active membrane 49 of the isolation diaphragm 42.The weld stress and heat affected zone of the weld area are removed fromthe interface where the integral diaphragm meets the thicker outer ring.All the weld stresses are at the tongue and groove arrangement, awayfrom the integral diaphragm. The stress resulting from the externalpressure N is a hoop stress, in compression, which closes the leadingends 80 a of the crack 80, preventing crack propagation. Thisapplication of compression rather than tension stress on the crack hasan effect similar to that of drilling a hole at the tip of a crack, toreduce the stress concentration on the crack tip (the crack tip is wherethe stress is highest, and is the initiating point for opening thecrack). Thus, this tongue and groove joining arrangement of the presentinvention improves on fatigue survival rates under cyclic pressureconditions, by moving the weld away from the thin member and preventingcrack propagation in the weld joint area. Furthermore, the increasedweld thickness, (T2 in the present invention of FIG. 6 versus T1 in theprior art of FIG. 5) allowed by the tongue and groove joiningarrangement, also provides a longer path to prevent the penetration ofhydrogen gas. The weld depth achieved with the tongue 48 acting as aheat block provides a thicker weld compared to butt welds. The longerweld depth prevents hydrogen permeability into the sensor, eliminatingnon-linearities in measurement, and potentially explosive situations.

As mentioned above, the tongue serves as a stop, thereby preventing thelaser or electron beam or other welding medium from penetrating furtherinto the joint. As can be seen in FIG. 5, the laser, electron beam orother welding medium may penetrate through the depth of the conventionalpartial depth butt weld 70, to the sensor cavity, thereby damaging thesensor or the wires. However, as can be seen in FIG. 6, the tongue 48blocks or shields the laser, electron beam or other welding medium andthereby preventing the same from penetrating to the sensor cavity of theheader 10.

The foregoing description of the embodiments of this invention has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the embodiments of the inventionto the form disclosed, and, obviously, many modifications and variationsare possible. Such modifications and variations that may be apparent toa person skilled in the art are intended to be included within the scopeof this invention as defined by the accompanying claims.

1. A pressure sensor header for a pressure transducer, the headercomprising: a header shell having a sensor cavity formed therein; asensor element disposed in the sensor cavity; a fluid medium disposed inthe sensor cavity; an isolation diaphragm closing the sensor cavity; ajoining arrangement disposed at an interface of the isolation diaphragmand the header shell, the joining arrangement joining the isolationdiaphragm with the header shell, the joining arrangement comprising: arecessed female joining element formed in one of the isolation diaphragmand the header shell; and a protruding male joining element formed onthe other one of the isolation diaphragm and the header shell, the malejoining element received in the female joining element.
 2. The pressuresensor header of claim 1, wherein the male joining element is formed onthe header shell and the female joining element is formed in theisolation diaphragm.
 3. The pressure sensor header of claim 1, whereinthe male joining element is formed on the isolation diaphragm and thefemale joining element is formed in the header shell.
 4. The pressuresensor header of claim 1, wherein the male and female joining elementshave mating rectangular cross-sections.
 5. The pressure sensor header ofclaim 1, further comprising a weld formed at the interface.
 6. Thepressure sensor header of claim 5, wherein the weld extends radiallyinward toward the joining arrangement.
 7. The pressure sensor header ofclaim 5, wherein the weld extends radially inward and bonds the elementsof the joining arrangement together.
 8. A pressure transducer assemblycomprising the pressure sensor header of claim 1 joined with a secondmember.
 9. The pressure transducer assembly of claim 8, wherein thesecond member comprises a sensor body.
 10. The pressure transducerassembly of claim 8, wherein the second member comprises a port.
 11. Thepressure transducer assembly of claim 8, further comprising a joiningarrangement disposed at an interface of the pressure sensor header andthe second member for joining the header with the second member, thejoining arrangement comprising: a recessed female joining element formedin one of the header and the second member; and a protruding malejoining element formed on the other one of the header and the secondmember, the male joining element received in the female joining element.12. The pressure transducer assembly of claim 1, wherein the isolationdiaphragm is an integral unit comprising a thin membrane surrounded by athicker outer ring.
 13. The pressure sensor header of claim 12, whereinthe male joining element is formed on the header shell and the femalejoining element is formed in the outer ring of the isolation diaphragm.14. The pressure sensor header of claim 12, wherein the male joiningelement is formed on the outer ring of the isolation diaphragm and thefemale joining element is formed in the header shell.
 15. The pressuresensor header of claim 12, wherein the male and female joining elementshave mating rectangular cross-sections.
 16. The pressure sensor headerof claim 12, further comprising a weld formed at the interface.
 17. Thepressure sensor header of claim 16, wherein the weld extends radiallyinward toward the joining arrangement.
 18. The pressure sensor header ofclaim 16, wherein the weld extends radially inward and bonds theelements of the joining arrangement together.
 19. A pressure transducerassembly comprising the pressure sensor header of claim 12 joined with asecond member.
 20. The pressure transducer assembly of claim 19, whereinthe second member comprises a sensor body.
 21. The pressure transducerassembly of claim 19, wherein the second member comprises a port. 22.The pressure transducer assembly of claim 19, further comprising ajoining arrangement disposed at an interface of the pressure sensorheader and the second member for joining the header with the secondmember, the joining arrangement comprising: a recessed female joiningelement formed in one of the header and the second member; and aprotruding male joining element formed on the other one of the headerand the second member, the male joining element received in the femalejoining element.
 23. A pressure sensor header for a pressure transducer,the header comprising: a header shell having a sensor cavity formedtherein; a sensor element disposed in the sensor cavity; a fluid mediumdisposed in the sensor cavity; and an isolation diaphragm closing thesensor cavity, the isolation diaphragm comprising an integral unithaving a thin membrane surrounded by a thicker outer ring.
 24. A methodof joining an isolation diaphragm with a header shell of a pressuresensor header, comprising the steps of: providing a protruding malejoining element on one of the header shell and the isolation diaphragm;providing a recessed female joining element on the other one of theheader shell and the isolation diaphragm; assembling the isolationdiaphragm to the header shell at a isolation diaphragm-header shellinterface so that the male joining element is disposed in the femalejoining element; and welding the isolation diaphragm and the headershell at the interface.
 25. The method of claim 24, wherein the weldingis performed with electron beam welding.
 26. The method of claim 24,wherein the male joining element is provided on the isolation diaphragmand the female joining element is provided in the header shell.
 27. Themethod of claim 24, wherein the male joining element is provided on theheader shell and the female joining element is provided in the isolationdiaphragm.
 28. The method of claim 24, wherein the male and femalejoining elements have mating rectangular cross-sections.
 29. The methodof claim 24, wherein the isolation diaphragm is an integral unitcomprising a thin membrane surrounded by a thicker outer ring.
 30. Themethod of claim 29, wherein the male joining element is provided on theouter ring of the isolation diaphragm and the female joining element isprovided on the header shell.
 31. The method of claim 29, wherein themale joining element is provided on the header shell and the femalejoining element is provided in the outer ring of the isolationdiaphragm.
 32. The method of claim 29, wherein the male and femalejoining elements have mating rectangular cross-sections.